The present invention relates to a multi-step flow cleaning method and a multi-step flow cleaning apparatus and, more particularly, to a multi-step flow cleaning method and a multi-step flow cleaning apparatus adapted to clean an workpiece by placing the workpiece, which has been treated with a chemical, in a cleaning tank and by supplying a cleaning solution thereby to clean the workpiece with the stream of the cleaning solution.
Hitherto, workpieces to be cleaned including semiconductor wafers, glass substrates, and electronic substrates are required to be subjected to a cleaning process for cleaning with a cleaning solution such as pure water to remove a chemical from the surfaces of the workpieces that have been subjected to a chemical treatment (etching). In this cleaning process, a cleaning apparatus is extensively used in which workpieces that have been subjected to the chemical treatment are placed, and a cleaning solution such as pure water is supplied from the bottom surface of the cleaning tank thereby to clean the workpieces by the stream of the cleaning solution.
FIG. 11 is a piping diagram showing the structure of a conventional cleaning apparatus adapted to clean workpieces with the stream of a cleaning solution by supplying the cleaning solution into the cleaning tank as described above.
As shown in FIG. 11, the conventional cleaning apparatus is provided with a cleaning tank 20 for holding workpieces (not shown) that have been treated with a chemical, a supply line 24 for supplying a cleaning solution such as pure water from the bottom surface of the cleaning tank 20, and a valve 22 connected at the middle of the supply line 24 to control the supply of the cleaning solution.
The valve 22 has a structure for opening or closing the supply line by electrically turning it ON or OFF. This enables the valve 22 to supply or interrupt the supply of the cleaning solution, which flows out through the supply line 24, to the cleaning tank 20.
When using the conventional cleaning apparatus, first, a plurality of workpieces, which have been subjected to a chemical treatment such as etching in a predetermined process, are placed in a cleaning cassette (not shown), and the cleaning cassette (not shown) is carried into the cleaning tank 20. When the cleaning cassette (not shown) has been carried into the cleaning tank 20, a cleaning solution such as pure water, which has been supplied through the supply line 24, is let flow into the cleaning tank 20 by opening the valve 22.
FIG. 12 is a graph showing changes in the flow of the cleaning solution supplied while the conventional cleaning apparatus shown in FIG. 11 is in the cleaning operation. As shown in FIG. 11, a constant flow of the cleaning solution is supplied into the cleaning tank 20 at all times until the cleaning is finished after the valve 22 is opened. The cleaning solution supplied in the constant flow flows into the cleaning cassette (not shown) placed in the cleaning tank 20 to clean the surfaces of the workpieces by the stream of the cleaning solution.
Thus, the conventional cleaning apparatus has been cleaning the surfaces of the workpieces held in the cleaning cassette (not shown) with the constant flow by supplying the constant stream of the cleaning solution through the supply line 24 connected to the bottom surface of the cleaning tank 20.
The conventional cleaning apparatus is capable of removing some foreign matters, which have adhered to the surfaces of the workpieces during the chemical treatment, by the stream of the cleaning solution supplied to the cleaning tank; however, the stream of the cleaning solution supplied in the constant flow is not good enough to remove some persistent foreign matters on the workpieces. Hence, it has been difficult for the conventional cleaning apparatus to remove the foreign matters, which have adhered during the chemical treatment process, to a satisfactory level.
Further, the conventional cleaning apparatus requires a large quantity of a cleaning solution and a long cleaning time in order to fully remove persistent foreign matters, which have adhered to the surfaces of workpieces during a chemical treatment process. Hence, it has been difficult to reduce a cleaning solution or shorten the cleaning time in implementing satisfactory cleaning of workpieces.
It is an object of the present invention to solve the problems described above and to provide a multi-step flow cleaning method and a multi-step flow cleaning apparatus that are capable of cleaning workpieces more effectively with the stream of a cleaning solution and also capable of suppressing an increase in foreign matters adhering to the surfaces of the workpieces.
To this end, according to one aspect of the present invention, there is provided a cleaning method by placing workpieces in a cleaning tank and by supplying a cleaning solution so as to clean the workpieces with a flow of the cleaning solution, wherein the flow of the cleaning solution supplied to the cleaning tank is adjusted to change the stream during a cleaning operation, thus cleaning the workpieces with the changing stream of the cleaning solution. In this case, the flow of the cleaning solution supplied to the cleaning tank is either changed from a small flow to a large flow in steps or continuously changed from a small flow to a large flow. Further, the supply flow of the cleaning solution is held small at least until the workpieces are fully immersed in the cleaning solution supplied to the cleaning tank.
According to another aspect of the present invention, there is provided a cleaning apparatus for cleaning workpieces by placing the workpieces in a cleaning tank and by providing the cleaning tank with a supply line to supply a cleaning solution so as to clean the workpieces with the stream of the cleaning solution, the cleaning apparatus being provided with a supply line for supplying the cleaning solution to the cleaning tank, and a flow adjusting means which is provided on the supply line and which adjusts the flow of the cleaning solution supplied to the cleaning tank, wherein the flow of the cleaning solution supplied to the cleaning tank is adjusted by the flow adjusting means to change the stream so as to clean the workpieces by the changing stream of the cleaning solution.